Studies on the biology of reproduction in the cichlid Tilapia nilotica (L.): effects of steroid and trophic hormones on ovulation and ovarian hydration

The effects of intraperitoneal injections of cortical and ovarian steroids and trophic (mammalian) hormones on ovulation, ovarian hydration and the distribution of sodium ions in muscles and ovary was studied in Tilapia nilotica. Cortisol, corticosterone and oestradiol 17p (50–250 mg kg−1 B.W.) induced ovulation in a dose-dependent manner and increased the degree of hydration of muscle and ovarian tissues. The sodium ion content of muscles was reduced and that of ovaries increased following treatment with these hormones. Oestrone, oestriol and progesterone (60–245 mg kg−1 B.W.) failed to induce ovulation but produced the same types of effects on the water and sodium ion content of muscles and ovaries as the other steroids. Human chorionic Gonadotrophin, HCG, (1200–12 000 I.U. kg−1 B.W.) also induced ovulation and increased the degree of hydration of muscles and ovaries and increased the sodium ion concentration in ovarian and reduced that of muscle tissues. Pregnant Mare Gonadotrophin, PMG, in doses similar to those of HCG, did not induce ovulation in any of the treated fish and did not significantly alter the water or sodium ion content of muscles and ovaries.

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